Control circuits for vacuum tubes



April 13, 1948. c. VOLZ 2,439,680

CONTROL CIRCUITS FOR VACUUM TUBES Filed April 4, 1944 2 Sheets-Sheet 1 GI Gezzewaz op Z0 Drivel 212g CaPAxle. [9

T0 Brake Cylllngen Gene azopflpz'uen I CapAxle. 59*12Q Suppgy 66656] 65 w I g eggfji-lzfll/fl m M M INVENTOR C olz. P T5 Fm Z M r HIS ATTORNEY Patented Apr. 13, 1948 CONTROL CIRCUITS FOR VACUUM TUBES Carl Volz, Penn Township,

assignor to The Union pany, Swissvale, Pa., aicorporation of Pennsylvania Allegheny County, Pa.,

Switch & Signal Com- Application April 4, 1944, Serial No. "529,458

'7 Claims. 1

My invention relates to control circuits for vacuum tubes, and more particularly to control circuits for gas tubes.

A bias voltage is often applied to the grid of a vacuum tube to control the operating characteristics of the tube. For example, in gas tubes, such as thyratron tubes, a bias voltage is applied to a grid to control the firing of the tube, thetube ordinarily being maintained non-conductive due to the bias voltagaand being fired when such bias voltage is removed or when a control voltage opposes and overcomes the-bias voltage. When such an arrangement is used in safety type circuits, such as railway signal and brake control circuits, it is essential to check the bias voltage because a failure of the bias voltage source or a brokencircuit element may result in the tube firing at a time when no control voltage is applied.

Because of such circumstances, a'feature of my invention is the provision of improved control circuits for vacuum tubes.

Another feature of my invention'is the provision of novel circuit arrangements to check the bias voltage of a vacuum tube.

A-specific feature of my invention is the provision of novel circuit arrangements for checking the'bias voltage of a gas tube used in safety circ-ui'ts such as rail-way signal and brake control circuits.

Other features, objects and advantages embodying my invention will appear as the specification progresses.

The foregoing features, objects and advantakes embodying my invention are accomplished by a vacuum tube circuit arrangement which includes a bias voltage source and the circuits lead to the associated grid element in series with the anode or plate circuit current source. Thus a loss or failure of the bias voltage source or a "broken circuit element through which the bias voltage is applied results in an open circuit condition for the anode circuit and the tube cannot be fired, and the load element which is interposed in the anodecircult cannot be energized to eifect a control that usually follows the energization of such load element due to a control-voltage applied to the tube.

I shall describe several forms of apparatus embodying my invention, and shall then point out the novel feature thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one form of apparatus embodying my invention-when the apparatus is used'ln railway'trainbrake decelostat equipwire l0, winding of of transformer Tl ment to preventslippin'g of car wheels. Fig. 2 is "a diagrammatic view showing another form of apparatus embodying my invention and wherewith both half cycles of an alternating current are used to energize the load element, the apparatus being-disclosed as used with train brake decelostat equipment. Fig. 3 is a diagrammatic view showing another form of apparatus embodying-my invention when two tubes are poweredfrom a common source and control a common load element buteach is controlled from an individual control voltage source, the apparatus being disclosed in connection with train brake decelostat equipment. Fig. 4 is a diagrammatic view showinga form of apparatus embodying my invention whentwo tubes having separate control voltages and load elements are powered through a common transformer, this form of apparatus also being disclosed in connection with railway train brake decelostat equipment. Fig. 5 is a diagrammatic view showing a form of apparatus embodying my invention when direct current sources are employed and the apparatus is used with railway train brake decelostat equipment.

It isto beunderstood that my invention is of general application and is not limited to train brake decelostat equipment, this one use serving to illustrate themany places where apparatus embodying my invention is useful.

beach of the several views like reference characters designate similar parts.

Referring to Fig. 1, the reference character VI designates a gas tube having an anode 2, a cathode 3, a shield grid 4, a control grid 5 and a filament 6. Power for tube VI is obtained through a transformer Tl, a primary winding 1 of which is connected to a suitable source of alternating current indicated in the drawing by its terminals being designated BX and CX. Filament 6 isconnected to secondary Winding 8 of transformer TI and tube Vl is heated to be in an active condition. A combined anode and shield grid circuit for tube Vi can be traced from the right-hand terminal of secondary winding 9 of transformer Tl, as viewed in Fig. 1, through a magnet valve Ml of a railway car-brake decelostat equipment to be referred to-shortly, wire ll, anode 2 of tube VI, intervening tube space to cathode 3 of the tube, wire l2, right-hand terminal of a secondary winding l3 winding I3 to its left-hand terminal, wire N, terminal iii of shield grid 4 of tube VI, and wire IE to the left-hand terminal of secondarywinding 9. It is clear that secondary windings S and I3 are connected in this circuit in series and are disposed for their instantaneous voltages to oppose each other. Thus, the voltage applied between anode 2 and cathode 3 tending to fire the tube is the resultant voltage of windings 9 and I3, and the shield grid 4 is provided with a bias voltage with respect to cathode 3 which is equal to the voltage created in winding IS. The two windings 9 and I3 are so proportioned that the voltage of winding 9 is relatively large as compared to the voltage provided by winding I3, and there is a resultant voltage applied to anode 2 tending tofire the tube each positive half cycle of the alternating current. It is apparent that duringthe positive half cycle of the resultant voltage applied to anode 2, the grid 4 is negative in potential with respect to cathode 3, and the instantaneous value of this bias voltage reaches its peak value the instant the anode voltage reaches its peak value. Such a negative bias voltage prevents the tube from firing. Also, during the half cycle the bias voltage applied to grid 4 is positive, the resultant voltage applied to anode 2 is negative with respect to cathode 3 and the tube is not fired. It follows, therefore, that normally the tube VI is maintained non-conductive due to the bias voltage applied to shield grid 4. The voltages for windings 9 and I3 are preferably pre-selected so that the voltageapplied to anode 2 would be just a little below or substantially that required to fire the tube when the bias voltage is withdrawn so that a relatively small control voltage applied to control grid 5 fires the tube. It is apparent also that the bias voltage source from secondary winding I3 is present whenever there is an anode voltage tending to fire the tube because of the series arrangement of. the two windings 9 and I3. Furthermore, it is apparent that a break in a circuit element by which the bias voltage is applied, except for a break of grid iwithin the tube VI, causes an open circuit condition for the anode circuit and tube VI cannot be fired.

Control grid 5 of tube VI is provided with a circuit including resistors I1 and 26, wire I9 and cathode 3. A condenser I8 and a, generator GI in series are connected across resistor 20. Generator GI is a direct current. generator driven from an axle of a railway car by any one of the several well-known drive mechanisms. For example, generator GI maybe belt connected to the axle. Generator GI therefore develops a direct voltage, the magnitude of which is proportional to the rate of rotation of the associated Wheels and axle unit. It is clear that condenser i8 is charged at a voltage corresponding to the voltage supplied by generator GI and this voltage across condenser I8 increases and decreases in step with the increase and decrease of the rate of rotation of the wheels and axle unit associated with generator GI. The parts are so proportioned that the usual rate of acceleration and deceleration of the car on which the equipment is mounted is such that the charging current and the discharging current are low and only a small voltage drop is created across resistor 29 due to these currents. However, in case the rate of deceleration of the wheels and axle unit due to an excessive brakingcondition is of a predetermined value greater than the normal rate the discharge from condenser I8 through resistor 20 is correspondingly large and a relatively high voltage drop is createdacross resistor 29. j r

The circuit connection of generator GI is such 4 that the polarity of the voltage created thereby is that indicated by the plus and minus signs placed in the drawing, and consequently the voltage drop created across resistor 20 by the discharge of condenser I8 is such that the top terminal of resistor 20 as viewed in Fig. 1 is positive with respect to the lower terminal and the control grid 5 of tube VI is driven positive in potential with respect to cathode 3 by this control voltage. This control voltage is of a value such that it overcomes the normal bias voltage applied to grid 4, and thus tube VI is fired when the rate of deceleration of the respective wheels is excessive. With tube VI fired current flows in the anode circuit each positive half cycle of the alternating current and magnet valve MI is energized, the energizati-on of magnet valve MI continuing during the period of discharge from condenser I8. As soon, however, as the control voltage created across resistor 20 by the discharge of condenser I8 ceases, the tube VI is deionized and magnet valve MI is deenergized. A condenser CI is preferably connected across magnet valve MI to improve the operation.

The decelostat of which magent valve MI isa part is of an arrangement that magnet valve MI when energized cuts ofi the supply of air pressure to the brake cylinder for the pair of wheels for the wheels and axle unitassociated with generator GI, and the brake cylinder is connected to atmosphere to release the brake of that pair of wheels. The parts are so proportioned that the control of tube VI by the discharge from condenser I8 and the energization of magnet valve MI continue for a period sufiiciently long to assure release of the brake and the wheels permitted to again rotate at the rate corresponding to the rate of rotation of the other wheels of the train.

It is to be seen, therefore, that in Fig, 1, apparatus is disclosed by which a normal bias voltage applied to tube VI to avoid its firing is checked by a series arrangement of a combined anode and shield grid circuit, and a loss of the bias voltage source or a broken circuit element by which the bias voltage is applied to the tube results in an open circuit condition for the anode circuit and the tube cannot be fired and the load element interposed in the anode circuit cannot be energized.

It should be noted in connection with the apparatus of Fig. 1 that the control voltage can be applied to grid d and the normal bias voltage applied to grid 5, and the same operation of the tube effected. p

In Fig. 2, equipment to use both half cycles of the alternating current for energizing the load element is disclosed. A second gas tube V2, similar to tube VI, is provided, and the two tubes VI and V2 are powered through the same transformer T2 and are controlled through the same source of control voltage. A primary winding 38 of transformer T2 is connected to the terminals BX and CK of the alternating current source. Filaments 6 and 25 of tubes VI and V2, respectively, are connected to secondary winding 39 of transformer T2 to heat the tubes. Since the load element is to be energized by both half cycles of the alternating current and both tubes are to be fired from the same source of control voltage, the voltages applied to the anodes of the two tubes must be of opposite relativepolarity. This results in a difierence of potential between the cathodes of the two tubes and their control grids cannot be connected to a commoncontrol source with a secon'dary winding 26' having a mid terminal for applying to the twotubes anode voltages of opposite relative polarityandwith a secondary winding 31 toapply to the control grids l of the tubes avoltage-thatvaries with the voltage variation between the --two "cathodes.

Tube VI= is providedwith an anode-shield gridcircuit extending froma left-hand terminal of secondary winding-2'3 through wire-27, anode 2 and tube-spaceto cathode-3 of tube VI, a secondary-windingiZB of transformer T2, wire 29, terminal I5 ofshield grid d of tube VI, wire 30, winding of magnet valve MI and wire 3| to mid terminal of secondary winding 26. Thus the left handportion-of secondary winding 26 serves as a source of anode voltage for tube VI and secondary-winding 28 serves as a source of bias voltage for the tuba-and these'two windings are seriallyincluded in thecircuit and are connected for their voltages to oppose each other, the parts being proportioned for tube VI to be normally maintained non-conductive.

IubeVZ isprovided with an anode-shield grid circuit extendingfrom the right-hand terminal ofsecondarywinding 26.through wire 32, anode 2| and tube space to cathode 22 of tube V2, secondary-winding of transformer T2,-wire 34, terminal 35 of-shield grid 23 of tube V2, wires 36and 30, windingofmagnet valve MI andwire :3I1to the mid terminal of-secondarywinding 23.

Thus the right-hand portion of secondary windw ing :25 servesasa source of anode voltage and secondary winding 33serves as a source of bias voltage for tube V2, the parts being so proportioned andthe connection such that the voltages of these two windings oppose each other and the tube V2 is normally maintained nonconductive. 'Also,-it is to be noted that the presence of the bias voltage for tube V2 is checked due to the series connection of the bias voltage rwinding 33 .and the anode voltage winding 26.

-It is also to be noted that the two biasing secondary windings 28 and 33 are serially connected'between the cathodes 3 and 22 of the two tubes VI and V2 and consequently there is a difference of potentialbetween these two cathodes equal to the sum of the two bias voltages. Secondary winding 31 of transformer T2 is connected between control grid 5 of tube VI and control grid :24 of tube V2 and is proportioned and connected so that the value of the voltage supplied to the control grids from secondary winding 31 is equal and is of opposite relative polarity to that existing between the two cathodes due to the series arrangement of the biasing windings 28 and 33. In this way, the control grid oi? each tube is normally at the same alternating current potential as its cathode. Tubes VI and V2 are provided with a source of control voltage that includes generator GI, the connection being similar to that shown and described for Fig. 1. That is, generator GI is driven from an axle of a car truck and serves as a source of control voltage through condenser I8 which is normally charged at a voltage'corresponding to that created bygenerator GI.

Normally, that is, when no effective voltage drop is created across resistor 23 of Fig. 2, both tubes VI and V2 are nonconductive due to the :biasxvoltage applied to their'respective shield -grids. In case the-wheel-of the wheels and axle unit associated with generator GI- are braked excessively and a resultant control voltage is created across resistor 23 due to the discharge of condenser I8,this control voltageis applied to control grid 5 of tube VI 7 and that tube is firedduring thepositive half cycles of thevoltage applied to its anode -2 and magnet valve-MI is energized by such half cycle of-anode current. This control voltage across resistor 20 isalso-applied across control grid 24 and cathode 22 of tube-V2 through windings 37, 33 and 28- and tube'V2 isfired during the-half cycles of the alternating-current that the anode-of tube VZ-ispositive with respect to the cathodeand themagnet valve MI is energized by these half cycle-impulses o-f-anode current. Consequently, magnetvalve-MI' is energized by both half cyclesof the alternating current supplied through transformer T2. Magnet valve M I when energized controls the-brake cylinder-pressure for the wheelsof thewheels and axle unit associated with generator GI, the same as explained in connection with -Fig. 1.

It follows that in Fig-=2 thereis disclosed-apparatus wherewith both tubes VI and V2 are controlled from the same source'of control Voltage and the magnet'valve M i' included in the anode circuits of both tubes isenergized'by both half cycles of the alternating current-of the power source. Also, the bias voltage-source for each tube and the circuit elements'by-which the bias voltage is applied are checked by the series arrangement of the anode-shield grid circuit of the respective tube In Fig. 3, tubes VI and-V2 arepowered through a common transformer,and are controlled from separate sources of control voltage to control in turn a common load element. A transformer T3 has a primarywinding 63 connected to terminals BX and CX of the alternating current source. Filaments ii and 25 are connected to secondary winding SI of transformer T3 to heat tubes VI and V2. An anode-shield grid circuit for tube VI can be traced from an adjustable terminal 32 of secondary winding 63oftransformer T3 through windingof magnet valve MLwire G l, anode 2 and tube space to cathode'3 of tube Vi, an adjustable terminal 65 of secondary winding 66 of transformer T3, Wire 6?, terminal I5 for shield grid 4 of tube VI, wire 33,-terminal 35 for shield grid 23 of tube V2and wire 68 to the left hand terminal of secondary winding 63. Secondary winding 63 serves as a source of anode voltage and secondary winding 63 serves as a source of bias voltage for tube VI, these secondary windings being disposed to supply to the circuit voltages of opposite relative polarity and of val ues preselected to give anode 2 a voltage tending to fire the tube and shield grid ii a bias voltage suificient to normally maintain the tube nonconductive. The adjustable terminals 32 and 65 would preferably be in the form of multiple taps and serve as an aid in preselecting proper anode and bias voltages for the tube.

Tube V2 has an anode-shield grid circuit including adjustable terminal 62.0f secondary winding 33, winding of magnet valve MI, wires 34 and 63, anode 2I and tube space to cathode E2 of tube V2, adjustable terminal 65 and secondary winding 66, wire 31, terminal E5 of grid 4, wire 33, terminal 35 of grid 23 of tube V2 and wire 38 to secondary winding 33. Windings 33 and I33 serve as sources of anode and bias voltages, respectively, for tube V2 in the same manner they did for tube VI.

Control grid 5 of .tube VI .of Fig. 3 is governed to generator GI is driven from a second axle of I the truck, a first axle of which truck drives generator GI. Generator G2 is connected to a condenser 4I through a. resistor 43 to chargecondenser 4| at a voltage proportional to the rate at which the respective wheels and axle unit rotates. Resistor 43 and a resistor 42 form a control grid circuit for tube V2 as will be apparent from an inspection of the drawing. Magnet valve MI which is the load element for both tubes Vi and V2 control the air pressure supplied to the brake cylinder of the associated truck in the manner explained hereinbefore.

Normally, both tubes VI and V2 of Fig. 3 are nonconductive and magnet valve MI is deenergized. In the event the rate of deceleration of either pair of wheels of the truck exceeds the usual rate and slipping of that pair of wheels becomes likely due to the excessive braking of the wheels the voltage drop created across resistor 28 4 or 43 as the case may be serves to fire the respective tube and magnet valve MI is energized to release the brakes for that truck.

It follows that each of tubes VI and V2 of Fig. 3 is provided with a series circuit arrangement by which the normal bias voltage and the circuit elements through which such bias voltage is applied are checked.

In Fig. 4, tubes VI and V2 have separate sources of control voltages and separate load elements and are powered through a common transformer. Generator GI of Fig. 4 is driven by the axle of a truck of a car, the same as in previous cases and is associated with the control grid circuit for tube VI the same as explained in connection with Fig. 1.

Magnet valve MI which is the load element for tube VI is used to control the brakes for the wheels of the wheels and axle unit associated with generator GI the same as in Fig. 1. Generator G2, similar to generator GI, is driven from a second axle of the car truck or from an axle a second truck of the car and is associated with a control grid circuit for tube V2 and which control grid circuit includes resistors 42 and 43 and condenser 4|, the same as in Fig. 3. A magnet valve M2, similar to magnet valve MI, is the load element for tube V2 and magnet M2 controls the brakes for the wheels of the wheels and axle unit associated with generator G2, the same as magnet MI controls the brakes of the wheels of the wheels and axle unit associated with generator GI.

Tubes VI'and V2 of Fig. 4 are powered through a common transformer T4, a primary winding 45 of which is connected to terminals BX and CK of the alternating current source. Filaments 6 and 25 of Tubes VI and V2 are heated from a secondary winding 44 of transformer T4. Tube VI of Fig. 4 is provided with an anode-shield grid circuit that can be traced from an adjustable terminal 45 of a secondary winding 46 of transformer T4 through winding of magnet valve MI, anode 2 and tube space to cathode 3 of tube VI, adjustable terminal 4? of a secondary winding 48 of transformer T4, terminal I of shield grid 4 of tube VI, wire 49, terminal 35 of shield grid 23 of tube V2 and wire 59 to the left-hand terminal of secondary winding 45. Secondary windings 46 and 4B are included in this circuit in series and are connected so that their voltages 8 oppose each other and are proportioned through the adjustable terminals 45 and 41 to provide proper bias and anode voltages for tube VI, the tube VI normally being maintained non-conductive, the same as explained in the previous cases.

An anode-shield grid circuit for tube V2 extends from an adjustable terminal 5I of secondary winding 46 through winding of magnet valve M2, anode 2I and tube space to cathode 22 of tube V2, adjustable terminal 52 and secondary winding 48, terminal I5, wire 49, terminal 35 of shield grid 23 of tube V2, and wire 50 to the other terminal of secondary winding 46. Secondary windings 4'6 and 48 are included in this circuit for tube V2 in series and are connected to oppose each other and by means of adjustable terminals 5I and 52 the voltages are proportioned to provide the proper bias voltage and anode voltage for the tube so that tube V2 is normally maintained non-conductive.

Normally, that is, when no effective voltage drop is effected across either resistor 29 or resistor 43, each tube VI and V2 is non-conductive due to the bias voltage applied to the respective shield grids 4 and 23. In the case the wheels of the wheels and axle unit associated with generator GI have an excessive rate of deceleration, the control voltage created across resistor 20 is applied to grid 5 of tube VI and that tube is fired to energize magnet valve MI and release the brakes in the manner explained hereinbeiore. Similarly, if the wheels of the wheels and axle unit associated with generator G2 have an excessive rate of deceleration, a control voltage is created. across resistor 43 due to the discharge from condenser M and this control voltage is applied to control grid 24 of tube V2 and the tube is fired so that the magnet valve M2 is energized to release the brakes of the respective pair of wheels.

In Fig. 5, the apparatus is similar to the apparatus of Fig. 1, except direct current sources are provided in place of the alternating current source and a condenser means is connected to the anode circuit of tube VI to at times deionize the tube. Filament 6 of tube VI is heated from a battery 53. An anode-shield grid circuit for tube VI comprises positive terminal of a battery 54, winding of a relay RI, anode 2 and tube space to cathode 3 of tube VI, a bias battery 55, wire 56 to terminal I5 of shield grid 4, and wire 51 to the negative terminal of battery 54. Batteries 54 and 55 are poled to oppose each other as indicated by the plus and minus signs placed in the drawing and for battery 55 to provide a preselected negative bias voltage for grid 4 with respect to cathode 3 and for battery 54 to provide a preselected anode voltage. A condenser 02 and an inductance LI are connected across cathode 3 and anode 2 and condenser C2 is normally charged at a voltage equal to the resultant voltage of the two batteries. Furthermore, condenser C2 and the inductance LI are proportioned to provide an oscillatory circuit when tube VI is conductive. Control grid 5 of tube VI of Fig. 5 is connected to generator GI, the same as in Fig. 1.

Normally, that is, when no eiiective control voltage is created across resistor 28, tube VI is non-conductive and relay BI is deenergized. In the event the wheels of the wheels and axle unit associated with generator GI have an excessive rate of deceleration and an efiective voltage is created across resistor 20, the tube VI is fired and relay BI is energized and picked up by the anode current. With relay RI picked up to close orator GI front contact 53, a simple circuit is completed for magnet valve MI to be energized from batter 54; magnet valve Ml controlling the release of the brakes of the'wheels associated with genas explained hereinbefore.

When tubeVl is madeconductive, the condenser C2 discharges and the tube is deionized in the well-known manner. Relay Bi is now deenergized but this relay is provided with a slow release period so that magnet valve MI is retained energized for a period sufiicient to insure the release of the'brakes. In Fig. 5', the condenser I8 would be proportioned so that its discharge period would bej'ust suiiici'ent to effect flringof tube VI.

It isapparen'tthat'in' Fig. 5 there is disclosed a series arrangement of the bias and anode voltage sources for a vacuum tube and which arrangement checks the presence of the bias voltage source and the circuit elements through which the bias voltage is applied.

Again, it is tobe observed that the circuits-here disclosed for vacuum tubes are of general application and are not limited to train brake decelostat equipment but are of specific advantage when applied to such equipment.

Although I have herein shown and described several forms of control circuits for vacuum tubes embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination; a vacuum tube having an anode, a cathode and a first and a second grid; a load element, a power source of energy, a bias source of energy, said power energy source connected between a terminal of said anode and a terminal of said second grid and said bias energy source connected between a terminal of said second grid and a terminal of said cathode to form a series circuit between said anode and cathode, said power energy source and said bias energy source disposed and proportioned to provide a preselected conductive condition of the tube and which condition is checked by said series circuit, said load element interposed in said series circuit to be energized according to the current flowing in said series circuit as determined by the conductive condition of said tube, and a control source of energy connected between a terminal of said first grid and said cathode terminal to at times modify the preselected conductive condition of said tube.

2. In combination; a vacuum tube having an anode, a cathode and a first and a second grid; a load element, a power source of energy, a bias source of energy, said power energy source connected between a terminal of said anode and a terminal of said second grid and said bias energy source connected between said second grid terminal and a terminal of said cathode to form a series circuit between said anode and cathode, said power energy source and said bias energy source having opposing polarities and disposed for said second grid to have a preselected negative potential with respect to said cathode and said anode to have a preselected positive potential with respect to said cathode to preselect the corn ductive condition of said tube and which condition is checked by said series circuit, said load element interposed in said series circuit and energized according to the conductive condition 10 of said tube, and a control circuit including a source of control energy connected between a terminal of said first grid and said cathode terminalto control at times-the conductive condition of said tube to efiect a predetermined encrgization of said load element.

3. In combination; a gas tube having an anode, a cathode, a control grid and a shield grid; a bias source of electromotive force, a power source of electromotive force; an anode-shield grid circuit for said tube and including a terminal of said cathode, said bias source, a terminal of said shield grid, said power source and a terminal of said anode in the order named; said bias source and said power source poled and proportioned for said shield grid to have a preselected negative potential with respect to said cathode and for said anode to have a preselected positive potential'with respect to the cathode to preselect a non-conductive condition of said tube, a load element interposed in said anode-shield grid circuit, and a control circuit including a source of control electromotive force connected between a terminal of said control grid and said cathode terminal to at times fire said tube to effectively energize said load element.

4. In'combi'nation; agas type of vacuum tube having an anode, a cathode, a control grid and a shield grid; a transformer having a primary winding connected to an alternating current source, a first secondary winding of said transformer connected between said anode and said shield grid and a second secondary winding of the transformer connected between said shield grid and said cathode to form a series circuit between said anode and said cathode, said first and second secondary windings connected in said series circuit for their voltages to have opposite relative polarities and proportioned for said tube to be non-conductive, a load element interposed in said series circuit, and a control circuit including a source of control voltage connected between said control grid and said cathode to at times fire said tube to energize said load element.

5. In combination; a gas tube having an anode, a cathode and at least one grid; a, transformer having a primary winding connected to a source of alternating current, a first secondary winding of said transformer connected between said anode and said grid and a second secondary winding of the transformer connected between said grid and said cathode to form a series circuit between said anode and cathode and by which circuit said grid is made negative in potential with respect to said cathode during the half cycle of the alternating current said anode is made positive in potential with respect to the cathode for maintaining a normal non-conductive condition of the tube and which condition is checked by said series circuit.

6. In combination; a first and a second gas tube each having an anode, a cathode, a control grid and a shield grid; a load element, a transformer having a primary winding connected to a source of alternating current, a power secondary winding having a mid terminal for said transformer; a first anode-shield grid circuit including in series a terminal of said first tube anode, a first half portion of said power secondary winding, said load element, a terminal of said first tube shield grid, a first bias secondary winding of said transformer and a terminal of said first tube cathode; said first half portion of the power secondary winding and said first bias secondary winding poled for their voltages to have opposite relative polarities to'maintain said first tube nonconductive; a second anode-shield grid circuit including a terminal of said second tube anode, a second half portion of said power secondary winding, said load element, aterminal of said second tube shield grid, a second bias secondary winding of said transformer and a terminal of said second tube cathode; said second half portion of the power secondary winding and said second bias secondary winding poled for their voltages to have opposite relative polarities to maintain said second tube non-conductive, another secondary winding of said transformer connected between the control grids of said tubes to vary the potential of said control grids in step with the variation in potential between said cathodes due to said bias secondary windings, and a control source of electromotive force connected between the control grid and cathode of each of said tubes to at times fire said tubes to energize said load element by both half cycles of said alternating current as supplied by said power secpower battery, a terminal of said'shield grid, said bias battery and a terminal of said cathode; said power and bias batteries poled and proportioned to render said shield grid negative in potential with respect to said cathode and to render said anode positive'in potential with'respect to said cathode, said voltages preselected to maintain said tube non-conductive and said load element deenergized and which conditions are checked by said series anode-shield grid circuit, a control circuit including a source of control voltage connected between a terminal of said control grid and said cathode terminal to at times render said control grid positive in potential with respect to the cathode to fire the tube to energize said load element, and means including capacitance connected tosaid anode-shield grid circuit to deionize said tube. H j CARL VOLZ.

REFERENCES CITED V UNITED STATES PATENTS Number Name Date 2,366,618' Harrison Jan. 2, 1945 

